This invention relates in general to a nut for securing a machine component and more particularly to a locking nut which may be secured against rotation while maintaining considerable precision in its axial position and to a method of manufacturing the nut.
Locking nuts exist in a variety of configurations for securing machine components on spindles and shafts or in housings. One of the more important uses of locking nuts resides in holding bearings on spindles, particularly on spindles at ends of drive and steer axles for large trucks. The typical spindle on one of these axles projects through the hub to which a road wheel is secured. Two single row tapered roller bearings, which are mounted in opposition, are interposed between the spindle and hub to enable the hub to rotate with minimum friction on the spindle. The inner races or cones of the bearings fit around the spindle, while the outer races or cups fit into the hub. The spindle at its end has a thread over which a nut passes, and the position to which the nut is advanced determines the setting for the bearings. Most automotive bearings are set near a condition known as zero end play, whether it be with a very slight amount of end play or a very slight amount of preload, the latter being preferred. Too much end play detracts from stability, and the hub and the wheel may wobble, producing excessive seal wear. Moreover, excessive end play causes the load zone in each of the bearings to concentrate at a few rollers, and this may shorten the life of the bearings. Excessive preload, on the other hand, imparts more force to the bearings and may cause the bearings to fail early.
A variety of nuts exist for holding bearings in place on spindles, one of the most common being jam nuts. Basically two nuts thread over the spindle. The one comes against the bearing, whereas the other is turned down against the first or in effect is jammed against the first. The first nut brings the bearings to a desired setting, and when that setting is achieved that nut lies against the inboard flanks of the thread on the spindle, that is to say against the flanks which are presented toward the bearing. But when the second nut is turned down tightly against the first nut, the second nut drives the first nut slightly farther along the spindle--far enough to bring the thread of the first nut against the outboard flanks of the thread on the spindle. This changes the setting of the bearings and to compensate for this change is difficult indeed, since threads are not machined to close tolerances. Thus, the distance the first nut advances when the second nut is turned down against it cannot be predicted with any certainty, and this confines the use of jam nuts to the region of end play which can be measured with dial indicators. To go into preload with jam nuts creates the danger of overloading the bearings.
Unitary locking nuts exist, and some of these do not change the setting of the bearings. But most unitary nuts require substantial machine work and are expensive to manufacture. Moreover, they require quite a few thread convolutions, and as a consequence are too long for some applications where compactness is important.
For example, one unitary nut, which is sold under the trademark SPIETH and bears the model designations MSR, MSA and MSW, is machined from a single forging or from tube or bar stock to provide the nut with a thread and a configuration that enables it to lock up on a threaded spindle. But the machining requires the workpiece to be gripped twice in a chuck for turning, once from each end. This, in turn, increases the time and the machine tools required to produce the nut, and as a consequence the nut is quite expensive. Indeed, its expense has restricted its use primarily to precision machinery, such as machine tools. Moreover, it is quite long and thus requires a substantial length of shaft thread--more than exists at the ends of many truck spindles. One rarely finds this nut in automotive applications.
The present invention resides in a unitary locking nut which assumes a predictable position on a thread as it is secured against rotation. All of the turning operations on the workpiece from which the nut derives are performed while the nut is gripped at a single location by a chuck. The nut is quite compact, and thus occupies relatively few thread convolutions.
The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed.